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  • AC to DC

    Can anyone tell me how to convert 110 AC to 110 DC for an electric motor I would like to use for a tool post grinder I am making

  • #2
    It wont be "clean" DC, but should work for a motor. A bridge rectifier is what you need. Radioshack should sell the part, bout five bucks. I think the ones I bought from radioshack say 20 amps, but I dont think I would trust them for that.

    -jacob

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    • #3
      Eh, be careful with Radio Shack......

      I went looking there, when I was out of town and needed a bridge rectifier....

      All they had was 200V or below rated, which is NOT suitable for rectifying the line. You need to use a 400V bridge to avoid failure from line transients etc.
      1601

      Keep eye on ball.
      Hashim Khan

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      • #4
        You want to convert AC to DC with a bridge rectifier (Diodes). The DC voltage will be unregulated and very noisy so your want to use a large 120V capacitor to filter out the noise and you probably even want to then go into a DC to DC converter.

        The DC to DC converter will take the unregulated DC voltae and will output and regulate another DC voltage.

        -3Ph

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        • #5
          A bridge rectifier (square cube) will make unregulated DC. Adding in a capacitor will smoothe the waveform (Raw Dc humps look like a camels back visualized on a scope but add approxmiate 35-50% more voltage to the unregulated circuit when the capacitor bumps it up)
          The rectifier is really just 4 diodes connected in such a way as to always point the "more positive" current toward the Plus pole. It comes from either side. Ac changes polarity 60 times a second plus to negative, the rectifier redirects all the positive power one way and recieves the negative the other way. Make sense? On a schematic or wiring diagram It looks like arrows with flat bars denoting the anode side pointing toward the (+)

          Unregulated DC will run a motor way past it's nameplate speed and destroy it with inrush current. A dc drive or servo drive is the best way to control a dc motor. It regulates the current not to exceed motor specifications.

          A pWM device such as a DC drive or chopper circuit as a lot of robotic geeks like to call it can chop the power up into duty cycle waveforms much like alloting bits of power till the "speed setpoint" is satisfied. A true dc drive measures this and turns the power on and off according to power setting. The smarter ones even know when a motor stalls because the ripple current of the motor armature is not there pulsing the feedback circuitry.

          A servo drive has much more inside it. It has a digital encoder that looks like a shutter wheel or windmill that actually interupts a photo eye and tells the drive the motors exact position. If you pulse it say 100 times it adds power till it achieves 100 encoder pulses. A true servo has two channels on the encoder out of synch 90 degrees that can denote direction by the previous state of the photo-eyes.

          I'd read all I could on power supplies and how to make a motor function before I hooked anything up. It is a exciting world out there and now ONE chip does what a cubic yard of electronics used to do. I learned in the analog world. Once you let all the smoke out of a electrical device they just don't act the same from then on.

          Read Hoffmans recent post, it is pretty enlightening.

          David

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          • #6
            http://www.surpluscenter.com/item.as...tname=electric

            Check out that link...may be interesting.

            -Jacob

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            • #7
              Lot of this going on.... Must be the weather...

              ------------------
              Hoffman in Warner Robins Ga
              Techno-Anarchist

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              • #8
                Dear "Slim";

                Assuming you have a 120 VAC line, the PEAK voltage is 120 x 1.414 = 170v. The AVERAGE voltage is 120 x .9 = 108v. A motor or a transformer responds to the Average voltage; therefore your motor will run just fine with NO Capacitor after the rectifier, and it will think it has 108VDC applied to it. Because of the inductance of the motor, it tends to keep the current in it constant although the full wave rectified Voltage will vary. As to what voltage rating the bridge rectifier should have, 400V or 600V should work OK.

                Regards,
                Jack C.

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                • #9
                  Hmm.. seen this before. Person puts a grinding wheel on said angle grinder. Turns it on, wheel explodes sending rock through Lower stomach, upper torso making for a very long stay in hospital. Last time it was really bad, guy got midsection opened up like I done it with a kabar.
                  He turned to walk to First aid station, tripped in his own guts that had fell out on the not so clean floor.

                  My older brother the PE. Well he got the job right after that of settling for the insurance company for the grinding rock company. It states clearly the MAX RPM on the Rocks. He set up a dc drive/encoder/speed display and got a gross of rocks. Running them at max speed under heavy load inside a 3/4 plywood box "NOT ONE OF THE GROSS" from the same production batch failed.

                  Problem was, "modified equipment" turning rocks not suitable for the rpm. Seems vibration, overspeed and applied load breaks down the rock. In other words, it was directly a Worker's compensation case with "No Free money from the manufacturer". The manufacturer is responsible for producing a product that performs as quoted. The worker/company is responsible for being intelligent enough to use them as designed. The company is responsible for seeing the employee works safely. And the employee puts his "own" boots on each day. This is all negociable by the crooked judges and juries of the world thou. McDonalds hot coffee burned my lip.. WAHHHH..

                  BE SAFE. I got a "Owie" this week. Enough for all of us.

                  David

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